/**************************************************************************
***    
*** Copyright (c) 1995-2000 Regents of the University of California,
***               Andrew E. Caldwell, Andrew B. Kahng and Igor L. Markov
*** Copyright (c) 2000-2002 Regents of the University of Michigan,
***               Saurabh N. Adya and Igor L. Markov
***
***  Contact author(s): abk@cs.ucsd.edu, imarkov@umich.edu
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***                          Los Angeles, CA 90095-1596 USA
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***************************************************************************/





//! author="Max Moroz"

#ifndef _GRAY_PERMUT_H_
#define _GRAY_PERMUT_H_

#include "permut.h"

typedef unsigned char byte;

//: Uses recursion to generate the permutation of [size] elements
//  satisfy the rule of Gray Code.
class GrayTranspositionForPermutations
{
    byte* _current;
    byte* _end;
    unsigned _size;
    static byte* _tables[];
    void initTable(unsigned size);
    public:
        GrayTranspositionForPermutations(unsigned size);

        bool finished() const;
        // have we gone through all permutations?

        unsigned next();
        // the next transposition is (q, q+1)
        // where q is whatever the following method returns
        // note: permutation elements are indexed as 0,1,...,size-1
        // note: q will never exceed size-2)

        Permutation getPermutation() const;
        // obtain the permutation corresponding to the current state of the object
};


/**** IMPLEMENTATIONS ***/

inline
GrayTranspositionForPermutations::GrayTranspositionForPermutations(unsigned size)
{
    abkfatal(size>1, "GrayTranspositionForPermutations class requires size > 1");
    if (!_tables[size]) initTable(size);
    _size=size;          // only for getPermutation()!!!
    _current=_tables[size];
    _end=_current+abkFactorial(size)-1;
}

inline 
bool GrayTranspositionForPermutations::finished() const
{ return _current==_end; }

inline 
unsigned GrayTranspositionForPermutations::next() { return *_current++; }

#endif
